WO2021066067A1

WO2021066067A1 - Sliding structure for internal combustion engine

Info

Publication number: WO2021066067A1
Application number: PCT/JP2020/037294
Authority: WO
Inventors: 博幸田森; 肇安藤; 一巳諸井
Original assignee: 日本ピストンリング株式会社
Priority date: 2019-09-30
Filing date: 2020-09-30
Publication date: 2021-04-08
Also published as: CN113906208A; JPWO2021066067A1

Abstract

This sliding structure is for an internal engine having a cylinder and a piston, wherein: the cylinder has a plurality of indentations formed in a stroke center region that covers the whole or part of an inner wall surface of the cylinder between a bottom surface position of the ring groove of the lowermost piston ring at top dead center of the piston and a top surface position of the ring groove of the uppermost piston ring at bottom dead center of the piston; and at least part of the surface of this stroke center region that comes into contact with the piston rings is formed in such a manner as to have a central low-roughness region where a contour curve as measured with a probe-type surface roughness tester has an arithmetic mean roughness Ra of 0.140 µm or lower. Consequently, this configuration achieves higher fuel efficiency in relation to the dimple liner technique.

Description

Sliding structure of internal combustion engine

The present invention relates to a sliding structure of an internal combustion engine having a cylinder and a piston.

Conventionally, in an internal combustion engine having a cylinder and a piston, efforts have been made to reduce the sliding resistance (friction force) between the cylinder and the piston in order to improve fuel efficiency and reduce oil consumption. The applicant has developed a so-called dimple liner as a method for reducing the frictional force between the piston ring and the cylinder (see, for example, Japanese Patent No. 51559224), and has a plurality of recesses in the central region of the inner wall surface of the cylinder. By forming or the like, the sliding resistance during operation is reduced.

Although it is not known at the time of this application, further research by the present inventors has revealed that there is still room for further improvement in fuel efficiency of this dimple liner technology.

In view of such circumstances, the present invention aims to further improve fuel efficiency and reduce oil consumption of dimple liners.

The present invention that achieves the above object is a sliding structure of an internal combustion engine having a cylinder and a piston, wherein the cylinder is the lower surface of the ring groove of the lowest piston ring at the top dead center of the piston in the inner wall surface. A plurality of recesses are formed in the stroke central region that is all or part of the distance from the position to the upper surface position of the ring groove of the uppermost piston ring at the bottom dead center of the piston. In at least a part of the surface in contact with the piston ring in the above, a central low roughness region in which the arithmetic average roughness Ra of the contour curve measured by the stylus type surface roughness measuring machine is 0.140 or less is formed. It is a sliding structure of an internal combustion engine.

In relation to the sliding structure of the internal combustion engine, the arithmetic mean height Sa of the contour curved surface of the central low roughness region measured by the non-contact surface roughness measuring machine is 0.20 μm or less. To do.

In relation to the sliding structure of the internal combustion engine, the protrusion valley depth Svk of the central low roughness region measured by the non-contact type surface roughness measuring machine is 0.41 μm or less.

In relation to the sliding structure of the internal combustion engine, the height Spk of the protruding peak portion of the central low roughness region measured by the non-contact surface roughness measuring machine is 0.16 μm or less.

In relation to the sliding structure of the internal combustion engine, the level difference Sk of the core portion in the central low roughness region measured by the non-contact type surface roughness measuring machine is 0.53 μm or less.

In relation to the sliding structure of the internal combustion engine, the protruding peak height measured by the non-contact type surface roughness measuring machine in the central low roughness region is E (Spk), and the protruding valley depth is I. When (Svk) is set, the I / E is 2.6 or less.

In relation to the sliding structure of the internal combustion engine, the arithmetic mean roughness Ra of the contour curve of the central low roughness region measured by the stylus type surface roughness measuring machine is 0.120 μm or less. To do.

In relation to the sliding structure of the internal combustion engine, the central low roughness region is characterized by including the vicinity of the upper end edge and the vicinity of the lower end edge in the process central region.

In relation to the sliding structure of the internal combustion engine, the entire region at the center of the stroke is the central low roughness region.

In relation to the sliding structure of the internal combustion engine, the arithmetic mean roughness Ra of the contour curve measured by the stylus type surface roughness measuring machine in the central low roughness region may be 0.090 μm or less.

In relation to the sliding structure of the internal combustion engine, the kinematic viscosity (kinematic viscosity) in the central low roughness region is μ, the relative velocity with the piston is U, the contact load with respect to the piston is W, and the piston. When the friction coefficient between them is f and the evaluation parameter of the Stribeck diagram is defined as A = μ × U / W, the minimum value fmin of the friction coefficient f in the central low roughness region is the evaluation parameter A. Is achieved within the range of 0.0003 or less.

In relation to the sliding structure of the internal combustion engine, the minimum value fmin is characterized in that the evaluation parameter A is achieved within a range of 0.0001 or more.

In relation to the sliding structure of the internal combustion engine, the kinematic viscosity (kinematic viscosity) in the central low roughness region is μ, the relative velocity with the piston is U, the contact load with respect to the piston is W, and the piston. When the coefficient of friction between them is f and the evaluation parameter of the Stribeck diagram is defined as A = μ × U / W, the center low is within the range where the evaluation parameter A is 0.0003 or less. The friction coefficient f in the roughness region is 0.07 or less.

In relation to the sliding structure of the internal combustion engine, the kinematic viscosity (kinematic viscosity) in the central low roughness region is μ, the relative speed with the piston is U, the contact load with respect to the piston is W, and the piston. When the coefficient of friction between them is f and the evaluation parameter of the strikebeck diagram is defined as A = μ × U / W, the center low is within the range where the evaluation parameter A is 0.0003 or less. The piston and the cylinder in the roughness region are in a fluid-lubricated state.

In a friction test in a non-combustible state using a top ring, a second ring and an oil ring corresponding to the piston ring in relation to the sliding structure of the internal combustion engine, the rotation speed of the internal combustion engine is N (r / min). When the mean effective pressure for friction loss (FMEP) between the piston ring and the piston ring in the central low roughness region is T (kPa), the mean effective pressure T for friction loss in the central low roughness region is minimized. The value Tmin is characterized in that the rotation speed N is achieved within the range of 700 or less.

In relation to the sliding structure of the internal combustion engine, the minimum value Tmin may be characterized in that the rotation speed N is achieved within a range of 600 or less.

In a friction test in a non-combustible state using a top ring, a second ring and an oil ring corresponding to the piston ring in relation to the sliding structure of the internal combustion engine, the rotation speed of the internal combustion engine is N (r / min). When the mean effective pressure (FMEP) of friction loss between the piston ring and the piston ring in the central low roughness region is T (kPa), the number of revolutions N is 700 or less. The friction loss mean effective pressure T in the central low roughness region is 14 kPa or less.

In a friction test in a non-combustible state using a top ring, a second ring and an oil ring corresponding to the piston ring in relation to the sliding structure of the internal combustion engine, the rotation speed of the internal combustion engine is N (r / min). When the mean effective pressure (FMEP) between the piston ring and the piston ring in the central low roughness region is T (kPa), the rotation speed N is 700 or less. The piston and the cylinder in the central low roughness region are in a fluid lubrication state.

In relation to the sliding structure of the internal combustion engine, the arithmetic mean of the contour curve measured by the stylus type surface roughness measuring machine on the upper side of the inner wall surface above the upper edge of the central region of the stroke. An upper low roughness region having a roughness Ra of 0.140 μm or less is formed, and the upper low roughness region and the central low roughness region may be continuous.

Arithmetic of contour curve measured by a stylus type surface roughness measuring machine on the inner wall surface below the lower edge of the stroke central region in relation to the sliding structure of the internal combustion engine. A lower low roughness region having an average roughness Ra of 0.140 μm or less is formed, and the lower low roughness region and the central low roughness region may be continuous.

In relation to the sliding structure of the internal combustion engine, the surface of the central low roughness region may be uncoated.

According to the present invention, it is possible to achieve an excellent effect of improving fuel efficiency or reducing oil consumption.

It is sectional drawing along the axial direction of the cylinder liner applied to the sliding structure of the internal combustion engine which concerns on 1st Embodiment of this invention. (A) and (B) are development views showing a state in which the inner peripheral wall of the cylinder liner is expanded in the circumferential direction. It is sectional drawing in the direction perpendicular to the axis of the inner peripheral wall of the cylinder liner. (A) is a side view showing a piston and a piston ring applied to the sliding structure of the internal combustion engine, (B) is a partially enlarged cross-sectional view showing the piston and the piston ring, and (C) is a top ring. It is a partially enlarged cross-sectional view of, and (D) is a partially enlarged cross-sectional view of a second ring. (A) is a cross-sectional view of a two-piece type oil ring, and (B) is a cross-sectional view of a three-piece type oil ring. It is (A) Strivec diagram and (B) FMEP diagram concerning the sliding of a general internal combustion engine. It is sectional drawing which shows the friction unit measuring apparatus which measures the sliding state of a general internal combustion engine. (A) is a Strivec diagram for explaining the sliding structure of the internal combustion engine of the first embodiment, and (B) is a FMEP diagram of the sliding structure. It is a side view which shows the sliding process of a cylinder liner and a piston ring of the internal combustion engine. (A) and (B) are graphs showing fluctuations in the frictional force between the cylinder liner and the piston ring during one stroke of the internal combustion engine. (A) is a cross-sectional view along the axial direction of the cylinder liner applied to the sliding structure of the internal combustion engine according to the second embodiment of the present invention, and (B) is the sliding stroke of the cylinder liner and the piston ring. It is a side view which shows. It is sectional drawing along the axial direction of the cylinder liner which shows the example of the cylinder liner to which the microtexture technique is applied.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, the sliding structure of the internal combustion engine according to the first embodiment of the present invention will be described in detail. In the first embodiment, the case where the internal combustion engine is a diesel engine is illustrated, but the present invention is not limited to this, and can be applied to other types of internal combustion engines such as a gasoline engine.

As shown in FIG. 1, a plurality of recesses 14 are formed on the inner wall surface 12 of the cylinder liner 10 according to the internal combustion engine of the first embodiment. The recess 14 is formed in the stroke central region 20 on the inner wall surface 12. The stroke central region 20 is from the lower surface position of the ring groove of the lowest piston ring at the top dead center T of the piston 30 to the upper surface position of the ring groove of the highest piston ring at the bottom dead center U of the piston 30. Is the maximum, and all or part of the area is the area (here, the case where the entire area is the stroke central region 20 and the recess 14 is formed in the entire area is illustrated). If the region outside the stroke center region 20 is defined as the outer region 25, this outer region 25 includes the upper outer region 25A adjacent to the top dead center side of the stroke center region 20 and the lower death of the stroke center region 20. It is composed of a lower outer region 25B adjacent to the point side. When the piston 30 reciprocates in the cylinder liner 10, it repeatedly passes through the upper outer region 25A, the stroke center region 20, the lower outer region 25B, the stroke center region 20, and the upper outer region 25A in this order. The boundary between the upper outer region 25A and the stroke central region 20 is defined as the upper boundary 27A, and the boundary between the lower outer region 25B and the stroke central region 20 is defined as the lower boundary 27B.

Of course, it is possible to form a plurality of recesses 14 beyond the stroke central region 20, but from the viewpoint of oil consumption (LOC), the recesses 14 are limitedly formed inside the stroke central region 20. It is preferable to do so.

The recess 14 is arranged on the inner wall surface 12 of the process central region 20 so that at least one recess 14 exists in the cross section of any location in the direction perpendicular to the axis. That is, the recesses 14 are arranged so as to overlap each other in the axial direction. As a result, the outer peripheral surface of the piston ring passing through the stroke central region 20 always faces at least one recess 14. On the other hand, the recess 14 is not formed in the upper outer region 25A and the lower outer region 25B.

The shape of the recesses 14 is a square (square or rectangle) arranged diagonally with respect to the axial direction, and as a result, the entire plurality of recesses 14 are arranged in an oblique grid pattern. In this way, as shown in the developed view of FIG. 2A, when focusing on a specific recess 14, the lowest point 14b in the axial direction of the recess 14 is the highest in the axial direction of the other recess 14. It is located below the point 14a in the axial direction. In this way, since the plurality of recesses 14 overlap in the axial direction, the recesses 14 are always present in the cross section perpendicular to the axis at every place (for example, arrow A, arrow B, arrow C) in the central region 20 of the stroke. it can. Here, in the stroke central region 20, a plurality of recesses 14 having the same area are uniformly arranged in the surface direction (axial direction and circumferential direction).

As shown in the developed view of FIG. 2B, a plurality of recesses 14 having the same area may be arranged non-uniformly in the surface direction. Here, the area occupied by the plurality of recesses 14 in the circumferential band-shaped region 20P at the axial end of the stroke central region 20 is small, and the circumferential band-shaped region at the axial central portion of the stroke central region 20 is small. In 20Q, the area occupied by the plurality of recesses 14 is large.

The size and shape of the recess 14 are not particularly limited, but are appropriately selected according to the size and purpose of the cylinder and piston ring. For example, the recess 14 can be formed in a slit shape or a band shape so as to penetrate (or extend) in the cylinder axial direction of the stroke central region 20. On the other hand, from the viewpoint of cylinder airtightness, the maximum average length J (see FIG. 2A) of the recess 14 in the cylinder axial direction is the cylinder shaft of the piston ring (top ring) located at the highest position of the piston. It is preferably less than or equal to the directional length (width), specifically about 5 to 100% thereof. The average length J of the recesses 14 means the average value of the maximum axial dimensions of the plurality of recesses 14 when there are variations.

The maximum average length S of the recess 14 in the cylinder circumferential direction is preferably in the range of 0.1 mm to 15 mm, and preferably in the range of 0.3 mm to 5 mm. If it is smaller than these ranges, the effect of reducing the sliding area by the recess 14 itself may not be sufficiently obtained. On the other hand, if it is larger than these ranges, a part of the piston ring tends to enter the recess, and a problem such as deformation of the piston ring may occur.

As shown in FIG. 3, the maximum average length R (maximum average depth R) of the recess 14 in the cylinder radial direction is preferably in the range of 0.1 μm to 1000 μm, and preferably in the range of 0.1 μm to 500 μm. More preferably, it is set to 0.1 μm to 50 μm. If the maximum average length R of the recess 14 in the cylinder radial direction is smaller than these ranges, the effect of reducing the sliding area of the recess 14 itself may not be sufficiently obtained. On the other hand, if it is attempted to be larger than these ranges, processing becomes difficult, and problems such as the need to increase the wall thickness of the cylinder may occur.

Returning to FIG. 2, the average value of the minimum distance H in the cylinder circumferential direction between the recesses 14 adjacent to each other in the circumferential direction at the same position in the axial direction is preferably in the range of 0.05 mm to 15 mm, preferably 0.1 mm to 5 The range of 0.0 mm is particularly preferable. If it is smaller than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small to slide stably. On the other hand, if it is larger than these ranges, the effect of reducing the sliding area of the recess 14 itself may not be sufficiently obtained.

By the way, although it is different from the dimple liner in which a plurality of recesses are arranged so as to overlap in the axial direction, there is a microtexture technology for forming the same kind of recesses, so this will be briefly explained. As shown in FIG. 12, the microtexture is a state in which a region V in which a recess is formed and a region Z in which no recess is present do not overlap in the axial direction along the cylinder axial direction of the inner wall surface of the cylinder liner. The theory is that each time the piston ring moves on the inner wall surface, engine oil flows in and out of the recess, and the dynamic pressure thickens the oil film and reduces the frictional force. .. The present invention is also applicable to such a microtexture technique. That is, the present invention reduces the contact area with the piston ring by forming a plurality of recesses (including hairline-shaped and scratch-shaped recesses due to honing processing, etc.) in the central region of the stroke. If it is a structure, it can be effectively applied.

On the inner wall surface 12 of the cylinder liner 10, the surface roughness (arithmetic mean roughness of the contour curve) measured by a stylus type surface roughness measuring machine (JIS B 0651: 2001) is provided in at least a part of the stroke central region 20. A central low roughness region 22 having a Ra (JIS B 0601: 2013)) of 0.140 (μm) or less, and preferably a surface roughness Ra of 0.120 (μm) or less is formed. Specifically, the surface roughness Ra of the surface of the inner peripheral surface 12 that can come into contact with the piston ring 40, that is, the surface of the inner peripheral surface 12 excluding the recess 14, is 0.140 (μm). The central low roughness region 22 is formed by the following processing, more preferably 0.120 (μm) or less. In this embodiment, the surface roughness (arithmetic mean roughness of the contour curve) measured by the stylus type surface roughness measuring machine is displayed as Ra, and is measured by the non-contact type surface roughness measuring machine described later. The three-dimensional surface roughness (arithmetic mean height of contour curved surface (JIS B 0681-2: 2018, ISO 25178-2: 2012)) is displayed as Sa.

The central low roughness region 22 is more preferably set to a surface roughness Ra of 0.090 (μm) or less, specifically 0.083 (μm).

Regarding this central low roughness region 22, a non-contact surface roughness measuring machine using a laser microscope conforming to JIS B 0681-6: 2014 (ISO 25178-6: 2010) (measurement magnification 1080 times, field size 259. Three-dimensional surface roughness value when measured at 4 μm × 259.4 μm, no cutoff, height direction (Z direction) measurement pitch 0.06 μm) (JIS B 0681-2: 2018, ISO 25178-2: 2012) Is shown below.
Arithmetic mean height Sa (μm): 0.192 or less, preferably 0.163 or less, more preferably 0.120 or less (specifically set to 0.110).
Overhang height Spk (μm): 0.159 or less, preferably 0.144 or less, more preferably 0.121 or less (specifically set to 0.116).
Core level difference Sk (μm): 0.521 or less, preferably 0.449 or less, more preferably 0.340 or less (specifically, set to 0.315).
Overhang valley depth Svk (μm): 0.409 or less, preferably 0.342 or less, more preferably 0.241 or less (specifically set to 0.218).

In particular, in the present embodiment, not only the height of the protruding ridge is reduced, but also the depth of the protruding valley is positively reduced to reduce the frictional force during sliding. By the way, in the conventional cylinder liner, in order to secure the holding force of the lubricating oil, it is necessary to increase the depth of the protruding valley portion to some extent, and accordingly, it is difficult to reduce the height of the protruding peak portion, and the sliding There is a limit to the reduction of frictional force inside. On the other hand, in the present embodiment, since the lubricating oil is sufficiently held in the adjacent recess 14, the contact surface itself with the piston ring 40 can sufficiently form an oil film even if the holding force of the lubricating oil is small. To this effect, when the height of the protruding peak is E and the depth of the protruding valley is I, the value of I / E is set to 2.6 or less in the central low roughness region 22 of the present embodiment. It is preferably set, more preferably 2.4 or less, and even more preferably 2.0 or less.

Further, in the present embodiment, the entire range of the surface that can come into contact with the piston ring 40 in the stroke central region 20 is defined as the central low roughness region 22. As a result, the central low roughness region 22 includes the vicinity of the upper end edge and the vicinity of the lower end edge of the process central region 20 in which the recess 14 is formed. Further, in the upper outer region 25A adjacent to the top dead center side of the stroke central region 20, an upper low roughness region 23A having a surface roughness Ra of 0.120 (μm) or less is formed, and the stroke central region region A lower roughness region 23B is formed for the lower outer region 25B adjacent to the bottom dead center side of 20. The upper low roughness region 23A, the central low roughness region 22, and the lower low roughness region 23B are completely connected in a uniform surface roughness state, and form an integral continuous surface as a whole.

Since the relative speed U of the cylinder liner 10 and the piston 30 decreases in the vicinity of the upper end edge and the vicinity of the lower end edge of the stroke central region 20, it is easy to shift from the fluid lubrication region to the boundary lubrication region. However, due to the presence of the central low roughness region 22, the fluid lubrication region can be predominantly developed. Since the so-called dimple liner technique can exert its effect in the fluid lubrication region, the advantages of the dimple liner technique can be obtained also in the vicinity of the upper end edge and the lower end edge of the process central region 20. It is also possible to form the central low roughness region 22 by limiting it to the vicinity of the upper end edge and / or the lower end edge of the stroke central region 20, but as in the present embodiment, the stroke central region It is preferable to form the central low roughness region 22 over the entire 20. When the relative speed U of the cylinder liner 10 and the piston 30 becomes lower, the boundary lubrication region approaches the center side of the stroke central region 20, but even in that case, fluid lubrication It is possible to expand the range of the area.

The central portion low roughness region 22 of the inner wall surface 12 of the cylinder liner 10 is formed by performing honing processing using a honing machine. At this time, it is preferable to use abrasive grains (JIS R 6001-2: 2017, ISO8486-2: 2007) finer than F500 or # 800 for the particle size of the honing grindstone.

Further, after the central portion low roughness region 22 is formed by this honing process, it is preferable not to perform a film treatment on the surface thereof. For example, when a phosphate film or the like generally used in the manufacturing process of the cylinder liner 10 is applied, the surface texture of the central low roughness region 22 varies depending on the film.

4 (A) and 4 (B) show the piston 30 and the piston ring 40 (top ring 50, second ring 60, oil ring 70) installed in the ring groove of the piston 30. The piston ring 40 reciprocates in the cylinder axial direction with the outer peripheral surface 42 facing the inner wall surface 12 of the cylinder liner 10. The top ring 50 eliminates the gap between the piston 30 and the cylinder liner 10 and prevents a phenomenon (blow-by) in which compressed gas escapes from the combustion chamber to the crankcase side. Like the top ring 50, the second ring 60 also has a role of eliminating a gap between the piston 30 and the cylinder liner 10 and a role of scraping off excess engine oil adhering to the inner wall surface 12 of the cylinder liner 10. The oil ring 70 scrapes off excess engine oil attached to the inner wall surface 12 of the cylinder liner 10 to form an appropriate oil film, thereby preventing seizure of the piston 30.

As shown enlarged in FIG. 4C, the top ring 50 is a single annular member, and has a so-called barrel shape that is convex outward in the radial direction when the outer peripheral surface 52 is viewed in cross section. Specifically, both outer edges of the outer peripheral surface 52 in the cylinder axial direction are inclined toward the outside in the cylinder axial direction in a direction away from the inner wall surface 12. The width f of the outer peripheral surface 52 with respect to the inner wall surface 12 of the cylinder liner 10 is preferably formed to be, for example, 0.3 mm or less. The surface roughness (arithmetic mean roughness Ra of the contour curve (JIS B 0601: 2013)) measured by the stylus type surface roughness measuring machine (JIS B 0651: 2001) of the outer peripheral surface 52 is 0.250. (Μm) or less is preferable.

As shown enlarged in FIG. 4D, the second ring 60 is a single annular member, and the vicinity of the outer circumference thereof has a tapered shape in which the diameter increases from the upper end in the cylinder axial direction toward the lower side in the cylinder axial direction. It has become. The outer peripheral surface 62 located at the outermost end of the tapered shape and in contact with the inner wall surface 12 of the cylinder liner 10 has a planar shape in a cross-sectional view. The contact width f of the cylinder liner 10 with respect to the inner wall surface 12 on the outer peripheral surface 62 is preferably formed to be, for example, 0.3 mm or less. The surface roughness (arithmetic mean roughness Ra of the contour curve (JIS B 0601: 2013)) measured by the stylus type surface roughness measuring machine (JIS B 0651: 2001) of the outer peripheral surface 62 is 0.250. (Μm) or less is preferable.

The tension of the top ring 50 and the second ring 60 is set to a relatively low value, and the surface pressure acting on the contact surfaces of the outer

peripheral surfaces

52 and 62 is, for example, 0.5 MPa or less, preferably 0.3 MPa. It becomes as follows. As a result, the top ring 50 and the second ring 60 often slide in the fluid lubrication region except for the vicinity of the top dead center and the vicinity of the bottom dead center.

The oil ring 70 enlarged and shown in FIG. 5 (A) is a two-piece type, and has a ring body 72 and a coil spring-shaped coil expander 76. The ring body 72 has a pair of

annular rails

73, 73 arranged at both ends in the axial direction, and an annular column portion 75 arranged between the pair of

rails

73, 73 and connecting them. The cross-sectional shape of the pair of

rails

73, 73 and the pillar portion 75 combined is substantially I shape or H shape, and by utilizing this shape, the coil expander 76 is accommodated on the inner peripheral surface side. An inner groove 79 having a semicircular arc shape is formed. Further, the pair of

rails

73 and 73 are formed with

annular protrusions

74 and 74 that project radially outward with respect to the pillar portion 75, respectively. The outer

peripheral surfaces

82, 82 formed at the tip of the

annular protrusions

74, 74 come into contact with the inner wall surface 12 of the cylinder liner 10. The coil expander 76 is housed in the inner peripheral groove 79 to press and urge the ring body 72 outward in the radial direction. A plurality of oil return holes 77 are formed in the pillar portion 75 of the ring main body 72 in the circumferential direction.

The contact width of each of the pair of outer

peripheral surfaces

82 and 82 in FIG. 5A is preferably formed to be 0.02 mm to 0.30 mm, and is set to, for example, 0.15 mm. The surface pressure acting on the contact surface of the outer peripheral surface 82 of the oil ring 70 is, for example, 1.0 MPa to 2.0 MPa, for example, about 1.75 MPa. Therefore, the oil ring 70 often slides in the fluid lubrication region when the engine speed is high, but often slides in the boundary lubrication region when the engine speed decreases. In FIG. 5A, the shape of the radial cross section of the outer

peripheral surfaces

82 and 82 is illustrated as a simple trapezoid, but the present invention is not limited to this, and the outer peripheral surface 82 of the upper rail 73 and the outer peripheral surface 82. On the outer peripheral surface 82 of the lower rail 73, the corners on the sides facing each other (coil expander 76 side) may be cut out in a step shape (so-called step land shape). The surface roughness (arithmetic mean roughness Ra of the contour curve (JIS B 0601: 2013)) measured by the stylus type surface roughness measuring machine (JIS B 0651: 2001) of the outer peripheral surface 82 is 0.450. (Μm) or less is preferable.

The oil ring 70 is not limited to the two-piece type, and may be, for example, the three-piece type oil ring 70 shown in FIG. 5 (B). The oil ring 70 has an

annular side rail

73a, 73b separated vertically and a spacer expander 76s arranged between the

side rails

73a, 73b.

The spacer expander 76s is formed by plastic working a steel material into a corrugated shape that repeats unevenness in the cylinder axial direction. Using this corrugated shape, an upper support surface 78a and a lower support surface 78b are formed, and a pair of

side rails

73a and 73b are supported in the axial direction, respectively. The inner peripheral side end of the spacer expander 76s has an ear portion 74 m that is erected in an arch shape toward the outer side in the axial direction. The selvage portion 74m abuts on the inner peripheral surfaces of the side rails 73a and 73b. The spacer expander 76s is incorporated into the ring groove of the piston 30 in a state of contraction in the circumferential direction with the abutment attached. As a result, the restoring force of the spacer expander 76s causes the selvage portion 74m to press and urge the side rails 73a and 73b outward in the radial direction.

The contact width f of each of the outer

peripheral surfaces

82 and 82 of the side rails 73a and 73b in FIG. 5B is preferably formed to be 0.02 mm to 0.40 mm.

Next, the friction mode between the cylinder liner and the piston ring will be described. The change in the coefficient of friction during general sliding is represented by the Strivec diagram shown in FIG. 6 (A). In this Strivec diagram, the friction mode of the solid contact region 110 that slides in direct contact, the friction mode of the boundary lubrication region 112 that slides through the oil-based coating, and the fluid lubrication region that slides through the viscous lubricating oil film. It is classified according to the friction mode in 114. Further, between the boundary lubrication region 112 and the fluid lubrication region 114, there is a friction mode of the mixed lubrication region 113 in which both states are mixed. In this Strivec diagram, the horizontal axis is a logarithmic representation of "kinematic viscosity (kinematic viscosity) μ" × "velocity U" / "contact load W", and the vertical axis is the coefficient of friction (f). ). Therefore, the frictional force can be minimized in the fluid lubrication region 114 or the mixed lubrication region 113, and effective utilization of these

regions

114 and 113 is effective for low friction, that is, low fuel consumption. On the other hand, if the speed U cannot shift from the middle of the boundary lubrication region 112 to the fluid lubrication region 114 even if the speed U increases, the boundary lubrication region 112 continues to the high-speed region as it is, as shown by the dotted line.

Incidentally, most of the frictional force of the fluid lubrication region 114 is the shear resistance of oil, and this shear resistance is defined by (viscosity) × (velocity) × (area) / (oil film thickness). As a result, reducing the shear area is directly linked to the reduction of frictional force.

Therefore, in the present embodiment, the oil is positively flowed into the contact surface of the outer peripheral surface 42 of the piston ring 40 to quickly shift to the fluid lubrication region 114 and realize low friction. At the same time, by applying the so-called dimple liner technique to the cylinder liner 10, a recess 14 is formed in the stroke central region 20 of the cylinder liner 10 to reduce the actual area where oil shear resistance is generated. Efficiently achieve a reduction in frictional force.

The Strivec diagram of FIG. 6A shows the dynamic change of the friction coefficient (f) during one stroke of the piston 40. As another index for evaluating the friction mode, the friction loss mean is used. There is effective pressure (FMEP: Friction Mean Effective Pressure). This friction loss mean effective pressure is the value obtained by dividing the friction work per cycle by the stroke volume. A diagram (FMEP diagram) of this friction loss mean effective pressure is shown in FIG. 6 (B). In the FMEP diagram, the horizontal axis is the rotation speed (N), and the vertical axis is the friction loss mean effective pressure (kPa). The higher the rotation speed (N), the greater the proportion of the fluid lubrication region 114 in one stroke. On the other hand, when the rotation speed (N) becomes low, the proportion occupied by the fluid lubrication region 114 in one stroke decreases, and the proportion occupied by the mixed lubrication region 113 (or the boundary lubrication region 112) increases. Therefore, the shape of the FMEP diagram of FIG. 6 (B) is relatively similar to the shapes of the fluid lubrication region 114 and the mixed lubrication region 113 of the Strivec diagram of FIG. 6 (A).

Next, the actual friction mode between the cylinder liner 10 and the piston ring 40 of the first embodiment will be described. Since the fixed positions of the top ring 50, the second ring 60, and the oil ring 70 installed on the piston 30 are relatively different in the cylinder axial direction, the friction state with the cylinder liner 10 is strictly different. Although slight differences occur in each piston ring, the position of the second ring 60 will be described here as the reference position of the piston ring 40. The top ring 50 is used as a reference only for the fastest passing point C.

FIG. 7 shows a friction unit measuring device 500 for measuring the friction mode between the cylinder liner 10 and the piston ring 50 adopted in the first embodiment. The friction unit measuring device 500 measures the friction state between the two by fixing the piston ring 40 side and reciprocating the cylinder liner 10 side up and down. That is, the measurement of this friction state is a friction test (non-combustion friction test) in a state where combustion as an internal combustion engine does not occur. The friction unit measuring device 500 holds a virtual piston 510 in which a piston ring 40 (three of a top ring, a second ring, and an oil ring) is set by a fixed shaft 514 via a load cell 512. The load cell 512 measures the external force (friction force) in the vertical direction acting on the piston ring 40.

The cylinder liner 10 is held by the moving sleeve 530 on the outer wall side thereof. The lower end of the moving sleeve 530 is held by the driving piston 540. The driving piston 540 is held by a connecting rod 550 that moves up and down by a crankshaft (not shown). As a result, the cylinder liner 10 reciprocates in the vertical direction. A fixed sleeve 560 is arranged on the outer circumference of the moving sleeve 530. The fixing sleeve 560 is fixed to the base 570. The fixed shaft 514 is fixed to the lid member 562 at the upper end of the fixed sleeve 560. The outer peripheral surface of the moving sleeve 530 and the inner peripheral surface of the fixed sleeve 560 are slidable. A temperature control jacket 565 is provided inside the fixed sleeve 560, and the temperature of the fixed sleeve 560 can be controlled by circulating hot water or cold water in the temperature control jacket 565.

In the present embodiment, as the measurement conditions of the friction mode by the friction unit measuring device 500, the standard of the lubricating oil is set to 10W-30, the oil temperature is set to 60 degrees, and the rotation speed of the crankshaft is changed from 215 rpm to 2154 rpm. ..

The height (width) of the top ring 50 was 2.5 mm, the surface roughness Ra of the outer peripheral surface 52 was set to 0.180 (μm), and the tension was set to 16.7 N. The height (width) of the second ring 60 was 2.0 mm, the surface roughness Ra of the outer peripheral surface 62 was set to 0.180 (μm), and the tension was set to 12.3 N. The oil ring 70 has a height (width) of 3.0 mm, and the surface roughness Ra of the outer peripheral surface 82 is set to 0.330 (μm) and the tension is set to 22.6N.

In order to analyze the friction mode of the first embodiment, the cylinder liner 10-A having the surface roughness Ra of the central low roughness region 22 set to 0.120 (μm) and the surface roughness Ra set to 0.083 ( A cylinder liner 10-B set to μm) was prepared, and the friction mode was measured using the friction unit measuring device 500. As a reference comparative example, a cylinder liner X having the same shape as the cylinder liner 10 and having a surface roughness Ra of 0.160 (μm) and a cylinder liner X having a surface roughness Ra of 0.160 (μm) without forming the recess 14 ( A cylinder liner Y set to μm) was prepared, the others were set under the same conditions, and the friction mode was measured using the friction unit measuring device 500. The measurement result of the Strivec diagram is shown in FIG. 8 (A), and the measurement result of the FMEP diagram is shown in FIG. 8 (B). Note that FIGS. 8A and 8B also show estimated values for a virtual cylinder liner K (surface roughness Ra0.140 (μm)) corresponding to the first embodiment.

First, a list of surface roughness of the cylinder liners 10-A, 10-B, and K is shown in Table 1 below. The arithmetic average roughness Ra is a value measured by a stylus type surface roughness measuring machine (JIS B 0651: 2001), and has an arithmetic average height Sa (μm) and a protruding peak height Spk (μm). , Projection valley depth Svk (μm), core level difference: Sk (μm) are values measured using a non-contact surface roughness measuring machine using the laser microscope described above.

In the cylinder liners 10-A and 10-B of the present embodiment and the cylinder liner X as a comparative example, a recess 14 is formed in the entire stroke central region 20. As shown in FIG. 9, the fluctuation of the coefficient of friction between the cylinder liner and the piston ring 40 when the piston 30 slides from the top dead center T to the bottom dead center U of the cylinder liner depends on the relative speeds of the two. .. This relative speed is uniquely determined with respect to the engine speed (rpm). The piston 30 descends from the state where the speed of the top dead center T of the cylinder liner 10 is zero, passes through the stroke A, and reaches the maximum speed C on the way. After that, when the bottom dead center U is reached via the process B, the speed becomes zero. During this time, the coefficient of friction constantly changes along the Strivec diagram of FIG. 8 (A).

In the Strivec diagram of FIG. 8A, the kinematic viscosity (kinematic viscosity) in the central low roughness region 22 is μ, the relative speed with the piston 30 (piston ring 40) is U, and the contact load with respect to the piston 30 is W. , The coefficient of friction with the piston 30 is defined as f (vertical axis of the graph), and the evaluation parameter is defined as A = μ × U / W (horizontal axis of the graph (logarial notation)).

In the cylinder liners 10-A and 10-B of the present embodiment, the minimum value fmin of the friction coefficient f in the central low roughness region 20 is located within the range where the evaluation parameter A is 0.0003 or less. More preferably, the minimum value fmin of the friction coefficient f is located within the range where the evaluation parameter A is 0.0002 or less. On the other hand, the minimum value fmin of the friction coefficient f in the central low roughness region 20 is located within the range where the evaluation parameter A is 0.0001 or more.

Further, in the cylinder liners 10-A and 10-B of the present embodiment, the friction coefficient f in the central low roughness region 20 is 0.07 or less in any of the ranges where the evaluation parameter A is 0.0003 or less. Become. Desirably, the friction coefficient f is 0.06 or less.

As can be seen from the comparison with the cylinder liner X (surface roughness Ra 0.160 (μm) / with recesses), the cylinder liners 10-A and 10-B of the present embodiment have a range in which the friction coefficient is 0.07 or less. , Spreads to the left side of the graph where the evaluation parameter A is 0.0003 or less. This means that even in low-speed sliding, the range of the fluid lubrication region 114 and the mixed lubrication region 113 is widened, and the sliding mode has an extremely low friction coefficient f.

For reference, in the case of cylinder liner X (surface roughness Ra 0.160 (μm) / with recesses), when the evaluation parameter A exceeds 0.0003, the effect of the recesses 14 appears and the rate of increase in the friction coefficient f increases. It decreases, and the friction coefficient f becomes smaller than that of the cylinder liner Y (surface roughness Ra 0.160 (μm) / no recess). On the other hand, when the evaluation parameter A is in the range of 0.0003 to 0.0005, the graph of the cylinder liner X (surface roughness Ra 0.160 (μm) / with recesses) and the cylinder liner Y (surface roughness Ra 0.160 (μm)) ) / Without recesses), and when the evaluation parameter A is 0.0003 or less, the friction coefficient f of the cylinder liner X (surface roughness Ra0.160 (μm) / with recesses) exceeds 0.07. Exceeds the friction coefficient f of the cylinder liner Y (surface roughness Ra 0.160 (μm) / no recesses). That is, in the case of the conventional cylinder liner X (surface roughness Ra 0.160 (μm) / with recess), the recess 14 acts to reduce the friction coefficient f in the range where the evaluation parameter A exceeds 0.0003. When the evaluation parameter A is in the range of 0.0003 or less, the recess 14 increases the friction coefficient f. According to an unknown consideration by the present inventors, in the case of the conventional cylinder liner X (surface roughness Ra 0.160 (μm) / with recess), the actual contact area between the cylinder liner and the piston ring 40 due to the presence of the recess 14 It is presumed that the lubrication shortage due to the lubricating oil is likely to occur in the low speed region, and the boundary lubrication region is likely to occur.

In the cylinder liners 10-A and 10-B of the present embodiment, the surface roughness Ra of the central low roughness region 20 is set to 0.120 (μm) or less, so that the evaluation parameter A is as low as 0.0003 or less. Even if the actual contact area with the piston ring 40 is small due to the recess 14 in the velocity region, the fluid lubrication region 114 or the mixed lubrication region 113 can be easily maintained. Further, even if the boundary lubrication state is reached, the friction coefficient is kept small because the surface roughness is small. Generally, when the surface roughness Ra of the inner peripheral surface of the cylinder liner is 0.120 (μm) or less, the holding force of the lubricating oil on the contact surface is lowered and it is easy to run out of lubricating oil. Since the recess 14 superposed on the central low roughness region 22 functions as a storage portion for the lubricating oil with respect to the central low roughness region 20, there is also a synergistic effect that the lubricating oil shortage is unlikely to occur in the central low roughness region 20. can get.

Further, in the cylinder liners 10-A and 10-B, the friction coefficient f in the range where the evaluation parameter A exceeds 0.0003 (high-speed region) is the cylinder liner X (surface roughness Ra0.160 (μm) / with recesses). It is close to or smaller than the coefficient of friction f of. That is, in the cylinder liners 10-A and 10-B, the central low roughness region 20 contributes to the reduction of the friction coefficient f even in the high speed region.

Although it is not an actual measurement value in the Strivec diagram of FIG. 8A, the surface roughness Ra of the central low roughness region 20 has the same configuration as the cylinder liner 10-A to 0.140 (μm). The friction coefficient of the set cylinder liner K is estimated and displayed. The friction coefficient of the cylinder liner K is the state of the conventional cylinder liners X and Y having a surface roughness Ra of 0.160 (μm) and the cylinder liner 10-A having a surface roughness Ra of 0.120 (μm). It can be inferred that it approximates the intermediate value of. Even with this cylinder liner K, the friction coefficient f in the central low roughness region 20 is 0.07 or less, preferably the friction coefficient f is 0, within the range where the evaluation parameter A is 0.0003 or less. It will be .06 or less. Further, in the cylinder liner K, the friction coefficient f in the range where the evaluation parameter A exceeds 0.0003 (high-speed region) is close to the friction coefficient f of the cylinder liner X (surface roughness Ra 0.160 (μm) / with recesses). Or less.

In the FMEP diagram of FIG. 8B, the mean effective pressure (FMEP) of friction loss between the central low roughness region 22 and the piston ring 40 is defined as T (kPa) (vertical axis), and the rotation speed of the internal combustion engine. Is defined as N (r / min) (horizontal axis).

In the cylinder liners 10-A and 10-B of the present embodiment, the minimum value Tmin of the average effective pressure T of friction loss in the central low roughness region 20 is located within the range where the rotation speed N is 700 or less. More preferably, the minimum value Tmin of the average effective pressure T of friction loss is located within the range where the rotation speed N is 600 or less.

Further, in the cylinder liners 10-A and 10-B of the present embodiment, the friction loss mean effective pressure T in the central low roughness region 20 is set to 14 kPa or less in any of the ranges where the rotation speed N is 700 or less. Set to.

As can be seen from the comparison with the cylinder liner X (surface roughness Ra0.160 (μm) / with recesses), the friction loss mean effective pressure T is smaller than 14 kPa in the cylinder liners 10-A and 10-B of the present embodiment. The range extends to 700 or less rotation speed N (on the left side of the graph). As a result, even at low rotation speeds, the sliding mode has extremely low friction loss.

As a reference, in the case of cylinder liner X (surface roughness Ra 0.160 (μm) / with recesses), when the rotation speed N exceeds 700 in a high rotation region, the effect of the recess 14 appears and the rate of increase in friction loss decreases. However, especially when the rotation speed N exceeds 1000, the friction loss becomes smaller than that of the cylinder liner Y (surface roughness Ra 0.160 (μm) / no recess). On the other hand, when the rotation speed N is in the range of 1000 to 1300, the graph of the cylinder liner X (surface roughness Ra0.160 (μm) / with recesses) and the cylinder liner Y (surface roughness Ra0.160 (μm) / without recesses) ) Graphs intersect. When the rotation speed N is 1000 or less, the friction loss of the cylinder liner Y (surface roughness Ra 0.160 (μm) / no recess) is exceeded, and when it is 700 or less, the friction loss increases in a range exceeding 14 kPa. That is, in the case of the conventional cylinder liner X (surface roughness Ra 0.160 (μm) / with recesses), the recess 14 acts to reduce the friction loss in the range where the rotation speed N exceeds 1000, but the rotation speed When N is in the range of 1000 or less, the recess 14 acts to increase the friction loss. According to an unknown consideration by the present inventors, in the case of the conventional cylinder liner X (surface roughness Ra 0.160 (μm) / with recess), the actual contact area between the cylinder liner and the piston ring 40 due to the presence of the recess 14 Therefore, it is presumed that insufficient lubrication due to the lubricating oil is likely to occur in the low rotation region, and the ratio occupied by the boundary lubrication region is likely to increase.

In the cylinder liners 10-A and 10-B of the present embodiment, the surface roughness Ra of the central low roughness region 20 is set to 0.120 (μm) or less, so that the rotation speed N is 700 or less in the low rotation region. Even so, the friction loss is suppressed by maintaining the fluid lubrication region 114 or the mixed lubrication region 113. Further, even if the boundary lubrication state is reached, the friction loss is suppressed because the surface roughness is small. Specifically, when the rotation speed N becomes 700 or less, the cylinder liner X (surface roughness Ra 0.160 (μm) / with recesses) is used as a reference, and in the case of the cylinder liner 10-A, about 2.0 kPa, the cylinder liner 10 In the case of −B, a reduction effect of about 4.0 kPa can be obtained. Generally, when the surface roughness Ra of the inner peripheral surface of the cylinder liner is 0.120 (μm) or less, the holding power of the lubricating oil is lowered and the lubricating oil is liable to run short. Since the recess 14 superposed on the roughness region 22 functions as a storage portion for the lubricating oil with respect to the central low roughness region 20, a synergistic effect that the lubricating oil shortage is unlikely to occur in the central low roughness region 20 can be obtained.

Further, in the cylinder liners 10-A and 10-B, the friction loss in the high rotation region where the rotation speed N exceeds 700 is close to the friction loss of the cylinder liner X (surface roughness Ra0.160 (μm) / with recesses). Or less. That is, in the cylinder liners 10-A and 10-B, the central low roughness region 20 does not adversely affect the friction loss even in the high rotation region.

By the way, this FMEP diagram is based on the friction test in the non-combustion state. Therefore, in the FMEP of the actual internal combustion engine in which the actual combustion occurs, the FMEP value is higher than this because the combustion pressure acts.

Although it is not an actual measurement value in the FMEP diagram of FIG. 8B, the surface roughness Ra of the central low roughness region 20 is set to 0.140 (μm) with the same configuration as the cylinder liner 10-A. The FMEP of the cylinder liner K to be made is estimated and displayed. The FMEP diagram of the cylinder liner K is the FMEP diagram of the conventional cylinder liners X and Y having a surface roughness Ra0.160 (μm) and the cylinder liner 10-A having a surface roughness Ra0.120 (μm). It can be inferred that it approximates the intermediate value of the FMEP diagram. Also in this cylinder liner K, the range in which the mean effective pressure T of friction loss becomes 14 kPa or less extends to 700 or less in rotation speed N (left side of the graph). As a result, even at low rotation speeds, the sliding mode has extremely low friction loss.

That is, in the cylinder liner K, friction loss is suppressed by maintaining the fluid lubrication region 114 or the mixed lubrication region 113 even in the low rotation speed region where the rotation speed N is 700 or less. Further, even if the boundary lubrication state is reached, the friction loss is suppressed because the surface roughness is small. Generally, when the surface roughness Ra of the inner peripheral surface of the cylinder liner is 0.140 (μm) or less, the holding power of the lubricating oil is lowered and the lubricating oil is liable to run short. Since the recess 14 superposed on the roughness region 22 functions as a storage portion for the lubricating oil with respect to the central low roughness region 20, a synergistic effect that the lubricating oil shortage is unlikely to occur in the central low roughness region 20 can be obtained.

FIG. 10A shows the fluctuation of the frictional force during the stroke of the cylinder liner X and the cylinder liner 10-B when the rotation speed N becomes 646 (low rotation speed). FIG. 10B shows fluctuations in the frictional force between the cylinder liner X and the cylinder liner 10-B during the stroke when the rotation speed N is 2154 (high rotation speed). The horizontal axis of these graphs is the phase (angle) of the connecting rod. It can be seen that during the low rotation operation of FIG. 10A, there is a large difference in the frictional force between the cylinder liner 10-B and the cylinder liner X. In particular, it can be seen that the difference in frictional force is large in the range of 45 to 135 degrees in phase in the process of moving to the top dead center side and in the range of 225 to 315 degrees in the phase of moving to the bottom dead center side. .. In particular, in the range of 180 degrees to 360 degrees in the process of moving to the bottom dead center side, the frictional force is significantly reduced over the whole. At low rotation, the cylinder liner X has a sliding mode close to the boundary lubrication region, but the cylinder liner 10-B is presumed to have a sliding mode close to the fluid lubrication region (or mixed lubrication region).

During the high rotation operation shown in FIG. 10B, the frictional force of the cylinder liner 10-B is generally smaller than the frictional force of the cylinder liner X. During high-speed operation, both the cylinder liner 10-B and the cylinder liner X are in the fluid lubrication region, and it can be seen that the frictional force of the cylinder liner 10-B is always smaller even in this fluid lubrication region. At the same time, it can be seen that the frictional forces near the bottom dead center of 0 degrees and 360 degrees, which tend to be the boundary lubrication region, and the phase of 180 degrees, which is the top dead center, are significantly reduced.

In the case of the sliding structure of the cylinder liner 10 and the piston 30 of the present embodiment, the oil consumption is also suppressed. This is because the absolute amount of the lubricating oil film formed in the central low roughness region 22 is reduced. Even if the absolute amount of the oil film is reduced, the recesses 14 are formed in an overlapping manner, so that the lubrication is not insufficient. That is, in the present embodiment, it is possible to rationally solve both the reduction of oil consumption and the sufficient lubrication effect. According to the simulations of the present inventors, in the case of a diesel engine, it was inferred that the LOC ratio of the cylinder liner 10-B was reduced by about 10% as compared with the cylinder liner X.

Next, the sliding structure of the internal combustion engine according to the second embodiment of the present invention will be described with reference to the attached drawings.

As shown in FIG. 11A, a plurality of recesses 14 are formed on the inner wall surface 12 of the cylinder liner 10 according to the internal combustion engine of the second embodiment. The recess 14 is formed only in the stroke central region 20 on the inner wall surface 12. This stroke central region 20 is located at the bottom dead center U of the piston 30 from the lower surface position 19A of the ring groove of the lowest piston ring at the top dead center T of the piston 30 (hereinafter, also referred to as the top dead center side edge). It is a part of the entire range (hereinafter, referred to as reference stroke area 19) up to the upper surface position 19B (hereinafter, also referred to as bottom dead center side edge) of the ring groove of the uppermost piston ring.

The stroke central region 20 of the present embodiment is located at a position shifted below the top dead center side edge 19A of the reference stroke region 19. As a result, a smooth upper smoothing region 130A having no recess is formed in the entire area from the top dead center side edge 19A of the reference stroke region 19 to the top dead center side edge 27A of the stroke central region 20. It is formed. The upper smoothing region 130A is a region through which the piston ring 40 passes.

Further, the stroke central region 20 of the present embodiment is located at a position shifted upward from the bottom dead center side edge 19B of the reference stroke region 19. As a result, a smooth lower smooth region 130B having no recess in the entire area from the bottom dead center side edge 19B of the reference stroke region 19 to the bottom dead center side edge 27B of the stroke center region 20. Is formed. The lower smoothing region 130B is a region through which the piston ring 40 passes.

In the present embodiment, the edge 27A on the top dead center side of the stroke central region 20 may be referred to as an "upper boundary" which means a boundary line between a place where the recess 14 is formed and a place where the recess 14 is not formed. Further, the edge 27B on the bottom dead center side of the stroke central region 20 may be referred to as a "lower boundary" which means a boundary line between a place where the recess 14 is formed and a place where the recess 14 is not formed. The lower dead center side edge (lower boundary) 27B of the stroke central region 20 may be aligned with the lower dead center side edge 19B of the reference stroke area 19 or may be extended to the lower side. Is also good.

Further, if the region outside the stroke central region 20 is defined as the external region 25, the external region 25 includes the upper external region 25A adjacent to the top dead center side of the stroke central region 20 and the stroke central region 20. It is composed of a lower outer region 25B adjacent to the bottom dead center side. The upper smoothing region 130A is included in a part of the upper outer region 25A, and the lower smoothing region 130B is included in a part of the lower outer region 23B.

In the present embodiment, the surface roughness (arithmetic mean roughness) Ra measured by the stylus type surface roughness measuring machine is 0.140 (μm) or less, which is preferable in at least a part of the process central region 20. Is formed with a central low roughness region 22 having a surface roughness Ra of 0.120 (μm) or less. Here, the entire process central region 20 is defined as the central low roughness region 22. As a result, the central low roughness region 22 includes the vicinity of the upper end edge and the vicinity of the lower end edge of the process central region 20 in which the recess 14 is formed.

The surface roughness value when the central low roughness region 22 is measured by a non-contact type surface roughness measuring machine using a laser microscope is shown below.
Arithmetic mean height Sa (μm): 0.192 or less, preferably 0.163 or less, more preferably 0.120 or less (specifically set to 0.110).
Overhang height Spk (μm): 0.159 or less, preferably 0.144 or less, more preferably 0.121 or less (specifically set to 0.116).
Core level difference Sk (μm): 0.521 or less, preferably 0.449 or less, more preferably 0.340 or less (specifically, set to 0.315).
Overhang valley depth Svk (μm): 0.409 or less, preferably 0.342 or less, more preferably 0.241 or less (specifically set to 0.218).

Further, in the upper smoothing region 130A adjacent to the upper side of the stroke central region 20, the surface roughness (arithmetic mean roughness) Ra is 0.140 (μm) or less by the stylus type surface roughness measuring machine, which is preferable. An upper low roughness region 23A having a surface roughness Ra of 0.120 (μm) or less is formed. The upper low roughness region 23A of the present embodiment is formed to a range beyond the upper smooth region 130A while being superimposed on the upper smooth region 130A. Further, in the lower smooth region 130 adjacent to the lower side of the stroke central region 20, the surface roughness (arithmetic mean roughness) Ra is 0.140 (μm) or less, and the surface roughness Ra is preferably 0. A lower low roughness region 23B of .120 (μm) or less is formed. The lower low roughness region 23B of the present embodiment is formed to a range beyond the lower smooth region 130B while being superimposed on the lower smooth region 130B. The upper low roughness region 23A, the central low roughness region 22, and the lower low roughness region 23B are completely connected in a uniform surface roughness state, and form an integral continuous plane as a whole.

The surface roughness values when the upper low roughness region 23A and / or the lower low roughness region 23B are measured by a non-contact type surface roughness measuring machine using a laser microscope are shown below.
Arithmetic mean height Sa (μm): 0.192 or less, preferably 0.163 or less, more preferably 0.120 or less (specifically set to 0.110).
Overhang height Spk (μm): 0.159 or less, preferably 0.144 or less, more preferably 0.121 or less (specifically set to 0.116).
Core level difference Sk (μm): 0.521 or less, preferably 0.449 or less, more preferably 0.340 or less (specifically, set to 0.315).
Overhang valley depth Svk (μm): 0.409 or less, preferably 0.342 or less, more preferably 0.241 or less (specifically set to 0.218).

When the piston 30 reciprocates in the cylinder liner 10, the upper outer region 25A (upper low roughness region 23A), the stroke central region 20 (center low roughness region 22), and the lower outer region 25B (lower low roughness region 25B) The cylinder region 23B), the stroke central region 20 (center low roughness region 22), and the upper outer region 25A (upper low roughness region 23A) are repeatedly passed in this order.

The stroke direction distance of the upper smoothing region 130 is preferably set to 30% or more of the total stroke direction distance of the reference stroke region 19. Further, the center point 20M in the stroke direction in the stroke center region 20 is located on the bottom dead center U side of the piston as compared with the center point 19M in the stroke direction in the reference stroke region.

When the position where the uppermost piston ring (top ring 50 described later) passes through the inner wall surface 12 at the maximum speed is defined as the fastest passing point C, the edge (upper boundary) on the top dead center side of the stroke central region 20 is defined. 27A is set to the fastest passing point C or less. In the present embodiment, the edge 27A on the top dead center side and the fastest passing point C are set to coincide with each other.

The central portion low roughness region 22, the upper low roughness region 23A, and the lower low roughness region 23B of the cylinder liner 10 are formed by performing honing processing using a honing machine. At this time, it is preferable to use abrasive grains (JIS R 6001-2: 2017, ISO8486-2: 2007) finer than F500 or # 800 for the particle size of the honing grindstone. After the central low roughness region 22, the upper low roughness region 23A and the lower low roughness region 23B are formed by this honing process, it is preferable not to perform a film treatment on the surface thereof. For example, when a phosphate film or the like generally used in the manufacturing process of the cylinder liner 10 is applied, the surface texture of the central low roughness region 22, the upper low roughness region 23A and the lower low roughness region 23B becomes a film. This is because it varies depending on the.

As already described, in the present embodiment, the upper low roughness region 23A in which the concave portion is not formed is provided on the upper dead center side of the central low roughness region 22 in which the concave portion is superposed. The significance of this upper low roughness region 23A is as follows. The top dead center side of the piston 30 is in a high temperature environment due to the existence of the combustion chamber. Therefore, if a recess is formed on the top dead center side of the cylinder liner 10 and the engine oil is retained in the recess, the engine oil becomes hot and vaporizes, so that the oil consumption increases. Therefore, in the upper low roughness region 23A, the oil consumption is suppressed by not forming the recess. On the other hand, if the upper low roughness region 23A is reduced in roughness as in the present embodiment, there is a possibility that lubrication may be insufficient, or the recess 14 formed so as to be superimposed on the central low roughness region 22 adjacent to the lower side may be formed. Since the lubricating oil functions as a storage portion for the lubricating oil and the lubricating oil is positively supplied to the upper low roughness region 23A through the recess 14, a synergistic effect that insufficient lubrication does not easily occur can be obtained.

Further, on the top dead center T side of the piston 30, the viscosity of the engine oil also decreases due to the high temperature environment, so that an oil film is difficult to form, but the surface roughness Ra is 0.120 (μm) or less due to the upper low roughness region 23A. , Preferably 0.100 (μm) or less, so that even a small amount of oil film is positively set as a fluid lubrication region or a mixed lubrication region. Even if the boundary lubrication region is reached, the roughness is low, so that the friction coefficient can be small. Further, since the lubricating oil accumulated in the recess 14 formed so as to be superimposed on the central low roughness region 22 can supply the lubricating oil to the upper low roughness region 23A, the lubricating oil shortage in the upper low roughness region 23A is unlikely to occur. There is an advantage.

FIG. 11B shows a process in which the piston ring 40 relatively moves the cylinder liner 10 from the top dead center T to the bottom dead center U. While the piston ring 40 moves relative to the upper low roughness region 23A, it becomes stroke lines A and L. Then, when the piston ring 40 passes through the central low roughness region 22, it becomes the stroke line M. After that, while the piston ring 40 is relatively moving toward the bottom dead center side in the lower low roughness region 23B of the cylinder liner 10, the stroke lines N and B are formed.

According to the sliding structure of the internal combustion engine of the second embodiment, the friction coefficient during low-speed movement can be reduced by the central low roughness region 22 as in the first embodiment. Further, it is possible to reduce the friction loss at low rotation speed. Further, the oil consumption can be suppressed by the upper low roughness region 23A through which the piston ring 40 passes.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

10 Cylinder liner 12 Inner wall surface 14 Recession 20 Stroke central area 22 Central low roughness area 23A Upper low roughness area 23B Lower low roughness area 25 External area 25A Upper outer area 25B Lower outer area 30 Piston 40 Piston ring 110 Solid contact area 112 Boundary lubrication area 113 Mixed lubrication area 114 Fluid lubrication area

Claims

It is a sliding structure of an internal combustion engine having a cylinder and a piston.
The cylinder
All or one of the inner wall surfaces from the lower surface position of the ring groove of the lowest piston ring at the top dead center of the piston to the upper surface position of the ring groove of the highest piston ring at the bottom dead center of the piston. Multiple recesses are formed in the central region of the stroke, which is the part.
Central low roughness such that the arithmetic mean roughness Ra of the contour curve measured by the stylus type surface roughness measuring machine is 0.140 μm or less on at least a part of the surface in contact with the piston ring in the central region of the stroke. Characterized by the formation of a region,
Sliding structure of internal combustion engine.
The arithmetic mean height Sa of the contour curved surface of the central low roughness region measured by the non-contact surface roughness measuring machine is 0.20 μm or less.
The sliding structure of an internal combustion engine according to claim 1.
The protrusion valley depth Svk of the central low roughness region measured by a non-contact surface roughness measuring machine is 0.41 μm or less.
The sliding structure of an internal combustion engine according to claim 1 or 2.
The protrusion height Spk of the central low roughness region measured by a non-contact surface roughness measuring machine is 0.16 μm or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 3.
The level difference Sk of the core portion of the central low roughness region measured by the non-contact surface roughness measuring machine is 0.53 μm or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 4.
When the height of the protruding peak portion measured by the non-contact type surface roughness measuring machine in the central low roughness region is E (Spk) and the depth of the protruding valley portion is I (Svk), the I / E is The feature is that it is 2.6 or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 5.
The arithmetic average roughness Ra of the contour curve of the central low roughness region measured by the stylus type surface roughness measuring machine is 0.120 μm or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 6.
The central low roughness region is characterized by including the vicinity of the upper end edge and the vicinity of the lower end edge in the process central region.
The sliding structure of an internal combustion engine according to any one of claims 1 to 7.
The entire central region of the stroke is the central low roughness region.
The sliding structure of an internal combustion engine according to any one of claims 1 to 8.
The kinematic viscosity (kinematic viscosity) in the central low roughness region is μ, the relative velocity with the piston is U, the contact load with respect to the piston is W, and the friction coefficient with the piston is f.
When defining the evaluation parameter of the Strivec diagram as A = μ × U / W,
The minimum value fmin of the friction coefficient f in the central low roughness region is characterized in that the evaluation parameter A is achieved within the range of 0.0003 or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 9.
The minimum value fmin is characterized in that the evaluation parameter A is achieved within the range of 0.0001 or more.
The sliding structure of an internal combustion engine according to claim 10.
The kinematic viscosity (kinematic viscosity) in the central low roughness region is μ, the relative velocity with the piston is U, the contact load with respect to the piston is W, and the friction coefficient with the piston is f.
When defining the evaluation parameter of the Strivec diagram as A = μ × U / W,
The friction coefficient f in the central low roughness region is 0.07 or less in any of the ranges in which the evaluation parameter A is 0.0003 or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 9.
The kinematic viscosity (kinematic viscosity) in the central low roughness region is μ, the relative velocity with the piston is U, the contact load with respect to the piston is W, and the friction coefficient with the piston is f.
When defining the evaluation parameter of the Strivec diagram as A = μ × U / W,
The piston and the cylinder in the central low roughness region are in a fluid-lubricated state within any range in which the evaluation parameter A is 0.0003 or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 9.
In a friction test in a non-combustion state using a top ring, a second ring, and an oil ring corresponding to the piston ring, the rotation speed of the internal combustion engine is set to N (r / min), and the piston ring in the central low roughness region. Friction loss between and when the mean effective pressure (FMEP) is T (kPa)
The minimum value Tmin of the friction loss average effective pressure T in the central low roughness region is achieved within the range where the rotation speed N is 700 or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 13.
In a friction test in a non-combustion state using a top ring, a second ring, and an oil ring corresponding to the piston ring, the rotation speed of the internal combustion engine is set to N (r / min), and the piston ring in the central low roughness region. Friction loss between and when the mean effective pressure (FMEP) is T (kPa)
The friction loss mean effective pressure T in the central low roughness region is 14 kPa or less in any of the ranges where the rotation speed N is 700 or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 13.
In a friction test in a non-combustion state using a top ring, a second ring, and an oil ring corresponding to the piston ring, the rotation speed of the internal combustion engine is set to N (r / min), and the piston ring in the central low roughness region. Friction loss between and when the mean effective pressure (FMEP) is T (kPa)
It is characterized in that the piston and the cylinder in the central low roughness region are in a fluid lubricated state within any range in which the rotation speed N is 700 or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 13.